1. Field of the Invention
The present invention relates to a method and an apparatus for data management through timer compensation in a wireless communication system. More particularly, the present invention relates to an apparatus and a method for compensating for a timer in order to minimize delay of a retransmission request for lost data.
2. Description of the Related Art
To guarantee in-sequence delivery of data in a Media Access Control (MAC) layer and a Radio Link Control (RLC) layer, an HSPA+ (HSPA evolution) has a structure in which the MAC layer performs reordering of the received data and then delivers sequential data to the RLC layer. At this point, when data is not received sequentially, the MAC layer buffers received data for in-sequence delivery of the data using a receiver window and a timer T1.
When data are not sequentially received in the MAC layer and the RLC layer, a reception end waits for reception of missing data for a predetermined time using a reordering release timer (referred to as a “timer T1” hereinafter). Data includes a unique Sequence Number (SN) for identifying between data. The SN is used for determining whether data is sequentially received or whether data lost in the midway exist.
The timer T1 controls stall avoidance in a reordering buffer of the reception end. An operating method of the timer T1 may be divided into four kinds as illustrated in FIG. 1A-1D.
FIG. 1A illustrates an exemplary start of a timer T1 according to the conventional art.
Referring to FIG. 1A, in the case where a Transmission Sequence Number (TSN) of received data is greater than a Next_Expected_TSN (NET) to be received next, the timer T1 is started when it is not activated, and T1_TSN is set to TSN of the received data. The T1_TSN is an SN of data arranged in order by a receiver window to trigger the timer T1 and not received. For example, when User Equipment (UE) receives data whose TSN is 0 and data whose TSN is 1 from a base station (Node B), a NET value becomes 2. After that, when the UE cannot receive data whose TSN is 2 from the Node B (that is, the data whose TSN is 2 is lost) and receives data whose TSN is 3, the UE compares the TSN of the currently received data with a current NET=2 to recognize that the data whose TSN is 2 has been lost and start the timer T1 (100). When the timer T1 is already activated, the timer T1 is not started and the existing already activated timer T1 is maintained. Since a 3 Generation Partnership Project (3GPP) specification defines that “only one timer T1 should maintain an activated state during a given time”, an additional timer is not started.
FIG. 1B illustrates an exemplary stop of a Timer T1 according to the conventional art.
Referring to FIG. 1B, when lost data (data whose TSN=2) exists and so the timer T1 starts (102) as in FIG. 1A and then UE receives data whose TSN=3, 4, a NET value maintains 2 and waits for next data. After that, when the UE receives data whose TSN=2 before the timer T1 expires, the UE stops the timer T1 and transmits data whose TSN is 2 to 4 to an upper layer (104). At this point, a NET value is updated as 5 and the UE waits for reception of data whose TSN=5.That is, when receiving lost data, the UE stops the activated timer T1.
FIG. 1C illustrates an exemplary expiration of the timer T1 according to the conventional art.
Referring to FIG. 1C, when lost data is not received for a predetermined time after a timer T1 is started (106) due to the lost data, the timer T1 expires (108). At this point, when T1_TSN is greater than NET, UE transmits received data (data whose TSN is 3 to data whose TSN is 9) having a TSN value between T1_TSN=9 and NET=2 to an upper layer. In addition, a NET value is set to a TSN value of data not received yet (for example, since up to data whose TSN is 9have been received, a NET becomes 10).
FIG. 1D illustrates an exemplary restart of a timer T1 according to the conventional art.
Referring to FIG. 1D, when the timer T1 is stopped or expires and in-sequence delivery of data to an upper layer is impossible, the timer T1 is restarted and T1_TSN is set to largest TSN of data which cannot be sequentially delivered.
For example, when data whose TSN=2 transmitted from a Node B is lost and UE receives data whose TSN=3, a NET value becomes 2 and T1_TSN indicating TSN of currently received data becomes 3. At this point, the timer T1 starts (110).
After that, UE receives data whose TSN=4 and TSN=8 (Here, it is assumed that data whose TSN=6 has been lost). At this point, a NET value maintains a TSN value (TSN=2) of lost data.
When the timer T1 stops or expires after the UE receives data whose TSN=8, currently received data (TSN=8) that cannot be sequentially delivered due to other lost data (TSN=6) is stored in a reordering buffer, so that the timer T1 is restarted with respect to TSN=6 (112). At this point, for the UE to expect retransmission of the lost data (TSN=6), a NET value is set to 6 and T1_TSN is set to 8. In addition, only data whose TSN=3 to TSN=5 are delivered to an upper layer.
As described above, the MAC layer of the HSPA+ starts/stops/expires/restarts the timer T1 using an SN of data in order to sequentially deliver packet data. At this point, for a T1 timer value, a value received from the upper layer is used.
Therefore, referring to the T1 timer restart procedure of FIG. 1D, when data whose TSN=2 is not received and data whose TSN=3 is received, the timer T1 starts. At this point, the timer T1 is set to a T1 timer value (for example, 100 ms) received from the upper layer. After that, when data whose TSN=2 is not received until the timer T1 expires, UE transmits relevant data (TSN=3,4,5) to the upper layer and restarts the timer T1 according to specification. At this point, the timer T1 is set with respect to data whose TSN=6. Even in this case, the timer T1 is set to a T1 timer value (for example, 100 ms) with respect to data whose TSN=2. That is, the T1 timer value should be applied and operated from a point where data whose TSN=6 has been lost but a timer T1 waits until a timer T1 that has been applied from a point where data whose TSN=2 has been lost expires, and then the timer T1 for the data whose TSN=6 operates, so that a retransmission request for the data whose TSN=6 is delayed.
Therefore, a method and an apparatus for reducing a delay in a retransmission request for other lost data at a point of starting a timer T1 after stoppage or expiration of the timer T1 in a wireless communication system are required.